Proteins having biological activities such as enzymes and antibodies immobilized on magnetic particles can be led by magnetic means. Therefore, they can be led to local positions at which it has been hitherto difficult for them to reach. Further, they can be collected and separated by means of a magnetic force. Thus they are expected to be utilized in various industries including the fields of medicine and fermentation.
In the prior art, for example, immobilization of biologically active substances to magnetic particles is disclosed in Japanese Patent Publication (KOKOKU) No. 6-12994. Namely, magnetic particles are separated from a magnetic bacterium by an alkaline treatment, and they are further treated with .UPSILON.-aminopropyltriethoxysilane or glutaraldehyde, and to them a biologically active substance is chemically immobilized. A method is also known, in which magnetic particles are separated by an enzyme treatment from a magnetic bacterium in a state of being covered with an organic thin membrane comprising lipid, and a protein is immobilized thereto after a treatment with glutaraldehyde. A method is also known in which a biologically active substance is immobilized on magnetic particles by a chemical binding method using SPDP (Japanese Pre-examination Patent Publication (KOKAI) No. 5-209884).
Further, methods for measuring antigens or antibodies have been proposed, in which an antigen-antibody reaction is allowed to occur by way of the magnetic particles to which a biologically active substance has been chemically immobilized by the aforementioned methods (Japanese Pre-examination Patent Publication (KOKAI) Nos. 4-285857, 5-209884, and 5-99926).
However, in any of the foregoings, it is necessary for a protein such as an enzyme of an antibody, etc. to be chemically bound, to magnetic particles. Thus poblems have arisen: a long time is required for the immobilization treatment; the biological activity of the protein is impaired; the amount of immobilized protein is greatly dispersed from one lot to another, and its biological activity is also greatly dispersed from one lot to another; and the immobilized protein inevitably becomes expensive because the protein to be used for immobilization is generally expensive.
Further, the aforementioned method in which labeled antibodies have been bound to magnetic particles before use makes it necessary that, in advance, a labeling substance is chemically bound or physically adsorbed to the antibodies. Because of this, the antibodies may lose its activity, or lose its fraction due to the treatment. Furthermore, the amount and binding mode of the labeling substance immobilized to the magnetic particles may vary, causing a variation in measurement data, which may, in turn, lead to an increased cost.
Accordingly, an object of this invention is to overcome the problems accompanying the conventional techniques in which an enzyme, antibody or labeling compound is immobilized to magnetic particles by a chemical method, and to provide a method enabling a high sensitivity measurement of a target substance, and magnetic particles to be used in that method.